Sound recording and reproducing system



April 9, 1938. A. c. KELLER ET AL 2,114,471

SOUND-RECOBDING AND REPRODUCING SYSTEM Filed June 20, 1936 2Sheets-Sheet 1 FIG.

INPUT '6 25 17 I8 26 INPU 16 No.5 y

VERTICAL LATERAL INVENTORS:A-C-KELLER $.RA FUSE BY ATTORNEY A ril 19,1938. A. c. KELLER ET AL 2,114,471

SOUND RECORDING AND REPRODUCING SYSTEM Filed June 20, 1936 2Sheets-Sheet 2 I 79 WI 7- 50 IG. 9

FIG. /2

By 5. RAFUSE Patented Apr. 19, 1938 UNITED STATES PATENT oFFi-rs SOUNDRECORDING AND REPRODUCING SYSTEM Application June 20, 1936, Serial No.86,228

7 Claims.

This invention relates to sound recording and reproducing systems andparticularly to those in which two separable recordings are made in asingle groove of a record.

In the systems of this general type proposed heretofore the tworecordings have usually been made as vertical and lateral undulationsrespectively. With a system of this type, however, it is very difficultto'obtain identical quality of reproduction from the two recordings.This may be due to differences in the frequency characteristics or inthe amplitudes of the distortion products of the two types of recorders,reproducers', or systems or it may be due to various other causes, butin any case the resulting quality differences in the two reproductionsare often quite apparent and they are particularly objectionable incases where the records are to be used forthe stereophonic reproductionof sound.

The object of this invention is to eliminate these quality differencesin the reproductions of multiple recordings in a single groove.

In accordance with the general features of the invention the tworecordings are formed by a 26 single stylus which vibrates in two planesat an angle to each other and at equal angles to its own axis and to thesurface of the record. In the preferred embodiment the planes ofvibration are normal to each other and at 45 degrees 80 to the surfaceof the record but they may be disposed at some other angle such as 60degrees, if desired, in which case each plane would also be inclined atan angle of 60 degrees to the surface of the record. The recorder mayconsist 35 of two suitable recorder units of any known type connected bysuitable linkages to the common stylus and the reproducer alsopreferably has two generating elements each responsive to undula tionsin only one of the groove walls so that the 40 two records may bereproduced separately without using external networks.

Since the recordings are disposed at the same angle to the recordsurface, quality differences may be substantially eliminated and forthis rea- 5 son the invention is particularly useful in stereophonicreproducing systems.

, The invention will be more clearly understood from the followingdetailed description and the accompanying drawings in which:

50 Fig. 1 is a schematic of a two-channel recording system according tothe invention in which the two recorder units are so disposed that eachunit drives the stylus in one of the recording planes;

M Fig. 2 is a schematic of an alternative recording system according tothe invention which utilizes any combination recorder adapted to cuthill-and-dale and lateral undulations in the same groove;

Fig. 3 shows the vibrating system of one type of vibration translatingdevice (recorder or reproducer) suitable for the system of Fig. 2;

Fig. 4 is a. vector diagram illustrating the operation of the device ofFig. 3; A

Fig. 5 shows the vibrating system of an electromagnetic type of recorderor reproducer suitable for the system of Fig. 1;

Figs. 6 and 7 show a cylindrical coil type recorder or reproducer forthe system of Fig. 1;

Fig. 8 shows another electromagnetic type of device for the system ofFig. 1; and

Figs. 9 to 12, inclusive, show aflat coil type recorder or reproducerfor the system of Fig. 1.

In the system of Fig. 1 two sources I5, 16 of 4 currents representingsound are connected "20 through amplifiers l1 and 18 to the windings l9and 20, respectively, of the recorder}! which has a single stylus 22 forforming a groove in the recording blank 23 on the turntable 24. It 7will be understood that the currents in the two 25 channels 25 and 26may be entirely unrelated or they may represent the same sounds asreceived at dilferent pick-up positions as ina stereophonic system ofany of the types discussed in Patent 2,019,616 to Maxfield, November 5,1935. 30

The recorder 2| has been shown diagrammatically to represent any one ofthe various types in which each recorder unit effects vibrations of thestylus in one recording plane independently of the other unit. In therecorder of Fig. 5, two balanced armature electromagnetic units 3|, 32of the general type disclosed in Patent 1,663,884 to Harrison, March 27,1928, are disposed sideby side. Extending upwardly at an angle of 45degrees (or any other desired angle a) from the shafts 33 and 34 onwhich the armatures 35 and 36 are mounted, there are driving arms 31, 38connected by linkages 39 and 4D to the stylus holder 4| in which ismounted the stylus 42. In order to restrain the stylus to move only inthe directions indicated by the lines 43 and 44 the stylus holder issecured to the stationary structure 45 of the recorder by a cantileverspring 46. g

When the currents representing the sounds to be recorded are supplied tothe windings l9 and 20 of the recorder units, the armatures 35 and 36will be vibrated in accordance with these currents as fully explained inthe Harrison patent referred to above. The linkage 39 will vibrate thestylus parallel to the line 43 and the linkage 40 will vibrate itparallel to the line 44 and since each linkage, as indicated in thedrawings, has a section of reduced stiffness at each end at whichbending can occur, each unit of the recorder may impart motion to thestylus without interfering with the driving action of the other unit. Asin the case of a single recorder unit, the stylus of this recorder willcut a plain or unmodulated groove of uniform depth when no current isapplied to either unit. When only the unit 3| is energized the stylus isvibrated at an angle of 45 degrees to the record surface along linesparallel to line 43 andwhen both units are energized the stylus willhave components of motion parallel to both of the lines 43 and 44.

Another type of recorder suitable for use with the system of Fig. 1 isshown in Figs. 6 and 'Z. In this construction the signal currents areapplied to the coils 5|, 52 which are mounted on the lightweight form 53on opposite sides of and at an angle .of 45 degrees (or any other angleon at which the recording planes are to be inclined to the surface ofthe recording material) to the tube 54 carrying the stylus 55. The coilsare disposed in the air-gaps 56 and 51 defined by the pole-pieces 58, 59and 60, SI and the necessary steady flux is set up in the air-gaps bythe ma nets 62, 63. The springs for supporting this vibratory system maybe of the type disclosed in Patent 2,027,168 to Harrison, January '7,1936, namely, a V-shaped cantilever upper spring 64 secured to thestationary structure by the screw 65 and riveted to the tube 54 so as tobe free to deflect both vertically and torsionally and a single wirespring 66 or its equivalent which stabilizes the system in its properposition.

Since the spring 64 is free to deflect both vertically and torsionallyand is of high lateral stiffness due to its V-shaped construction, thevibrations of the coils 5I and 52 due to the reaction of the signalcurrents with the flux in the air-gaps will produce a motion of thestylus which has both horizontal and vertical components as in thestructure previously described. The lines of the axes of the coils 5!and 52 pass below at the point of attachment of the pivot spring 6% sothat the coil 5| vibrates the stylus along lines parallel to line 68 andcoil 52 vibrates the stylus along lines parallel to line 69 and cuts aVshaped groove having recordings in two planes at equal angles to therecord surface.

A magnetic type recorder similar in operation to the moving coilstructure. just described is shown in Fig. 8. In this device atriangular form 47 carries two magnetic armatures 48 and 49 which aredisposed at right angles to each other and are driven by the signalcoils 50 on the polepieces of magnets 93. This vibrating system issupported by springs similar to those used for the device of Figs. 6 and'1 except that their relative position is preferably reversed, thesingle wire spring 04 being at the top and the V-shaped spring 95 beingintermediate the armature and the stylus 95. Under the faces set up bythe signal currents the system spring 95 will be deflected verticallyand torsionally as in the structure of Fig. 6, but in this case theleft-hand unit vibrates the stylus along line 97 and the right-hand unitvibrates it along line 98. 7

Another type of recorder suitable for the system of Fig. 1 is shown inFigs. 9 to 12. This device is a double fiat coil recorder which issomewhat similar in principle to the single coil reproducer disclosed inPatent 2,034,872 to A. C.

Keller, March 24, 1936. In this device the vibrating system is supportedby two spaced parallel cantilever springs, the upper spring II being asingle wire and the lower spring l2 being V- shaped to provide avertically resilient pivot as in the reproducer of the Keller patent.This recorder also has pole-pieces defining a working gap for onlyone-half of each of the coils l3 and I4 which are mounted on the tubularmember l5 carrying the stylus 16. The magnet I? supplies flux to thepole-pieces I3 and 14 which are mounted on the tubular member 15carrying the stylus Hi. The magnet 11 supplies flux to the polepieces 18and 19 which define the gaps 80, ill for the coils 13, I4. Thepole-piece 18 extends downwardly between the coils and presentspole-faces 82, 83 to the coils over their entire area but has a circularopening 84 opposite the coil core mem bers 85 and 86 to providevibrating clearance for the upper spring II. The extension piece 8'! ofthe pole-piece I9 presents a pole-face 88 to one diagonal half of thecoil I3 and the extension piece 89 of the pole-piece I9 presents apole-face S0 to the other diagonal half of the coil I l. The currents inthe coil 13 from one of the sources I5 or I6 will drive the movingsystem about the pivot spring I2 to impart motion to the stylus alonglines parallel to line 9|. Similarly, currents in the coil I4 will drivethe system to impart a vibratory motion to the stylus along linesparallel to line 92 and as in the case of the devices, previouslydescribed, both coils may drive the stylus simultaneously to produceseparate recordings in the two Walls of the groove.

The system of Fig. 2 produces a v-groove of the type already describedby means of a recorder adapted to cut hill-and-dale and lateralundulations in the same groove. One such recorder, as shown in Fig. 3,comprises two electromagnetic units IOI, I02 of the type disclosed inthe Harrison patent referred to above. In this recorder the shaft I03 ofthe unit IIlI has a horizontal arm I04 connected to the vertical arm I05which is secured to the stylus holder I06 and is adapted to drive thestylus I01 vertically to cut a hill- A5 and-dale record. The shaft I08of the unit I02 has a vertically depending arm I09 and a horizontal armIIO secured to the stylus holder I06 for driving the stylus laterally toproduce a lateral cut record. The arm IIO has a section of reducedstiffness at each end and the arm I05 has a similar section at its upperend so that both units may drive the stylus simultaneously withoutreacting on one another and the vibrating system is constrained to moveonly in the desired modes by the cantilever spring Hi.

In the system of Fig. 2 each of the sources H2 and H3 of signal currentsis connected through amplifiers II3 to H6 and volume controls II? to I20to both of the recording channels i2% and these two channels areconnected by the am plifiers I23 and I24 to the windings I25 and I23 ofthe units IGI and I02, respectively, of the recorder which is shown morein detail in Fig. 3. The volume controls II! to I20 are adjusted so thatthe energy from each signal source is divided between the two recorderunits in the proportions necessary to give equal vibratory amplitudes ofthe stylus in the two recording planes and the and 522.

connections from the two sources to the units are unit I02 will tend todrive it laterally so that the actual motion of the stylus due tosignals from either source will be in accordance with the resultant ofthese forces and will be at an angle of 45 degrees to the surface of therecord I 2?.

This will be more clearly understood from the vector diagram of Fig. 4in which the vectors are designated by prime numbers corresponding tothe amplifiers which tend to produce motion of the stylus in thedirection indicated. At a given instant the output of amplifier H3 willactuate the unit IIII of the recorder to drive the stylus downwardly asindicated by vector H3 and at the same instant the output of amplifierH4 will actuate unit I62 to move the stylus to the left as indicated bythe vector H4 so that the actual motion of the stylus at the instantchosen due to the currents from the source I I2 will be along the vectorI28 (Figs. 3 and 4) and corresponding undulations will be cut in thegroove I29. Similarly the output of amplifier H5 associated with thesource I32 will actuate unit IIII to move the stylus along the vectorH5, and the output of amplifier H6, being connected with relativelyopposite polarity to the channel I22 as compared with the connection ofamplifier I I4 to that channel, will actuate unit I02 to move the stylusalong vector H6, that is, in the direction opposite to that of vector II4'. The resultant of these two forces produced by the sounds from thesource H3 moves the stylus along the vector I30 and cuts undulations ingroove I29 which are normal to those produced by the source H2.

When no signal currents are applied to either unit of any of therecorders discussed above, each will cut a V-shaped groove of uniformcrosssection and of the average depth required to record the maximumamplitude variations without cutting out of the record material as inthe case of any conventional recorder. When signal currents are applied,the groove will remain symmetrical with respect to the line I3I so longas the horizontal components of the faces applied to the stylus by thetwo recorder units are equal and opposite. This condition would obtainwhen the signal currents in the two recording channels are identical andthe resulting recording would be merely a V-shaped hill-and-dale groove.

In practice, however, the two channels will carry currents whichordinarily differ in amplitude, frequency content, or phase relationshipor any combination of these difierences so that the resulting groovewill undulate both laterally and vertically and the undulations in onerecording plane will often be entirely different from those in the otherrecording plane.

The various structures shown in Fig. 3 and Figs. 5 to 12, inclusive,have been described as recorders, but it will be obvious to thoseskilled in the art that when proportioned according to Well-knownreproducer requirements they will also serve to reproduce bothrecordings in the groove simultaneously when connected to suitableamplifiers and loud-speakers.

While the principal advantage of this invention over the combinationhill-and-dale lateral system is its ability to give two reproductions ofidentical quality as required in certain applications such asthereophonic reproduction, the invention may be used in various otherways. For example, one of the recording units may be used to make arecord in which the volume range is compressed and the other unit maycut a control record to effect a complementary expansion in the volumerange during reproduction.

Since the two recordings have vertical components in common, surfacenoise in reproduction can be materially reduced by cutting a soundrecord in only one of the recording planes and feeding back in reversephase the output of the reproducer unit which is driven in the otherplane into the circuit of the reproducer unit which is reproducing therecorded sounds.

Various modifications of and other uses for the systems and apparatusdescribed Will occur to those skilled in the art, but the invention isintended to be limited only by the scope of the following claims.

What is claimed is:

1. In a sound recording system, a record member, a stylus for forminggrooves in the member, two stylus driving units having members vibratingin accordance with currents to be recorded and driving the stylussimultaneously in two planes at equal angles to the surface of therecord member.

2. A vibration translating device comprising a stylus, means forsupporting the stylus for vibration simultaneously in two planes atequal angles to the axis of the stylus, two vibration translating units,each having an element vibrating in one of the planes, and linkagesconnecting the elements to the stylus.

3. In a sound recording system, a record member, a stylus for forminggrooves in the member, means for supporting the stylus for vibrationsimultaneously in two planes at equal angles to the surface of themember, two sources of currents to be recorded, and means responsive tothe currents from each source for driving the stylus in one of theplanes.

4. In a sound recording system, a record memher, a hill-and-dalerecording unit, a lateral recording unit, a stylus, linkages connectingthe units to the stylus, two sources of currents to be recorded,unilaterally conducting circuits connecting each source to bothrecording units, and means in the circuits for varying the divisionenergy from each source between the recording units.

5. A vibration translating device comprising a stylus, means forsupporting the stylus for vibration simultaneously in two planes formingequal angles with the vertical axis of the stylus, two electromagnetictranslating units disposed on opposite sides of the stylus, a Vibratingarmature in each of the units, and a driving connection between thestylus and each of the armatures.

6. A vibration translating device having a moving system comprising astylus, a stylus holder and two coils mounted in spaced relation on theholder, means for producing a flux for each of the coils, and spacedparallel springs supporting the system for stylus vibrations in twoplanes forming equal angles with the vertical axis of the stylus.

7. In a sound recording system, a record member, a hill and dalerecording unit, a lateral recording unit, a common stylus for the units,linkages connecting the units to the stylus, two sources of currents tobe recorded, separate unilaterally conducting circuits supplyingcurrents of the same polarity from the sources to the hill and dale unitand separate unilaterally conducting circuits simultaneously supplyingcurrents of opposite polarities from the sources to the lateral unit.

ARTHUR C. KELLER. IRAD S. RAFUSE.

